Method for manufacturing organic semiconductor element

ABSTRACT

A method for manufacturing an organic semiconductor element, capable of obtaining an organic semiconductor element in which an organic semiconductor layer is easily patterned without being lowered in mobility, which includes: a source electrode and drain electrode formation step; an organic semiconductor layer formation step of forming an organic semiconductor layer having the liquid crystal organic semiconductor material on the alignment layer to cover the source electrode and the drain electrode; a dielectric layer formation step of forming a dielectric layer on the organic semiconductor layer to be positioned at least on a channel region between the source electrode and the drain electrode; and an annealing step of annealing the organic semiconductor layer, on which the dielectric layer is formed, at a liquid crystal phase temperature of the liquid crystal organic semiconductor material.

TECHNICAL FIELD

The present invention relates to an organic semiconductor element inwhich an organic transistor is formed on a substrate, and a method formanufacturing the element.

BACKGROUND ART

In recent years, about semiconductor transistors, typical example ofwhich are TFTs, the scope of articles to which the transistors are usedtends to be enlarged with the development of display devices. In such asemiconductor transistor, its electrodes are connected to each otherthrough the material of its semiconductor, so that the transistorfulfills a function as a switching element.

Hitherto, the semiconductor material used in the semiconductortransistor has been an inorganic semiconductor material such as silicon(Si), gallium arsenic (GaAs), or indium gallium arsenic (InGaAs). Inrecent years, semiconductor transistors in which such an inorganicsemiconductor material is used have been used in TFT array substratesfor display, the use of which has been spreading in liquid crystaldisplay devices.

As the semiconductor material, an organic semiconductor material made ofan organic compound has also been known. The organic semiconductormaterial is low in process temperature, so that the material can beformed on a flexible plastic substrate. Thus, the material hasadvantages that the material is stable against mechanical impacts, andcan be made light. Moreover, the material can be produced through acoating process such as printing, so that the material may bemass-produced into a larger area at lower costs than the inorganicsemiconductor material. Accordingly, the following activities in whichsuch organic semiconductor materials are objects have been activelymade: applications of the organic semiconductor materials tonext-generation display devices, such as flexible disks, typicalexamples of which are electronic papers; and researches in which printRFID tags and others are targeted.

At the time of manufacturing an organic transistor in which an organicsemiconductor material is used, it is usually necessary to pattern itsorganic semiconductor layer. As a method for patterning the organicsemiconductor layer, an ink-jetting method and others have beenreported. However, the methods require the step of forming ahydrophilic/hydrophobic pattern on a substrate, the step of formingpartition walls thereon, or some other step. However, there is caused aproblem that when the organic semiconductor layer undergoes such a step,this layer is declined in mobility.

Separately, attempts have been made for forming an organic semiconductorlayer on the whole of a surface and then forming a protective layerthereon, and further inactivating its portion not protected by theprotective layer as a mask, or removing the organic semiconductor layerpartially (see, for example, Patent Literatures 1 to 4). As a method forthe inactivation, investigations have been made about plasma treatment,the use of an oxidizer, and others. As a method for the removal,investigations have been made about laser radiation, and others.

However, when an organic semiconductor element is manufactured, thesemethods require its organic semiconductor layer to be patterned byinactivating or removing the organic semiconductor layer. Thus, theprocess thereof becomes complicated, and costs are increased.

Known is also a method of using a liquid crystal organic semiconductormaterial, and patterning an organic semiconductor layer byhydrophilic/hydrophobic patterning, a transferring method or some othermethod (see, for example, Patent Literatures 5 and 6).

CITATION LIST Patent Literatures

-   Patent Literature 1: WO 2006/048092 pamphlet-   Patent Literature 2: WO 2008/131836 pamphlet-   Patent Literature 3: Japanese Patent Application Laid-Open (JP-A)    No. 2008-277381-   Patent Literature 4: JP-A No. 2008-270494-   Patent Literature 5: JP-A No. 2005-294530-   Patent Literature 6: JP-A No. 2009-200479

SUMMARY OF INVENTION Technical Problem

In light of the above-mentioned actual circumstances, the presentinvention has been made, and a main object thereof is to provide anorganic semiconductor element manufacturing method capable of obtainingan organic semiconductor element in which an organic semiconductor layeris easily patterned without being lowered in mobility.

Solution to Problem

In order to attain the object, the invention provides a method formanufacturing an organic semiconductor element, comprising steps of: asource electrode and drain electrode formation step of forming a sourceelectrode and a drain electrode on an alignment layer for aligning aliquid crystal organic semiconductor material; an organic semiconductorlayer formation step of forming an organic semiconductor layer includingthe liquid crystal organic semiconductor material on the alignment layerto cover the source electrode and the drain electrode; a dielectriclayer formation step of forming a dielectric layer on the organicsemiconductor layer to be positioned at least on a channel regionbetween the source electrode and the drain electrode; and an annealingstep of annealing the organic semiconductor layer, on which thedielectric layer is formed, at a liquid crystal phase temperature of theliquid crystal organic semiconductor material.

According to the invention, the manufacturing method thereof has theannealing step, whereby the aggregate of the liquid crystal organicsemiconductor material is formed on the alignment layer and in thedielectric-layer-nonformed region, so that this region has no organicsemiconductor layer. By contrast, no aggregate of the liquid crystalorganic semiconductor material is formed on the alignment layer and inthe dielectric-layer-formed region thereof, so that this region has theorganic semiconductor layer. Thus, the organic semiconductor layer caneasily be patterned without being lowered in mobility. Additionally, theworkpiece is annealed at the liquid crystal phase temperature; thus, inthe organic semiconductor layer, the aligning treatment of the liquidcrystal organic semiconductor material can be simultaneously attained.

In the invention, the manufacturing method thereof may have, before thesource electrode and drain electrode formation step, an alignment layerformation step of using an electrode laminated body having a substrate,a gate electrode formed on the substrate and a gate insulating layer onthe substrate to cover the gate electrode, and forming theabove-mentioned alignment layer on the gate insulating layer of theelectrode laminated body. When the method has this alignment layerformation step, an organic semiconductor element of abottom-gate/bottom-contact type can be formed.

In the invention, it is preferred that the alignment layer is a layercapable of aligning the liquid crystal organic semiconductor materialvertically. When the alignment layer has this vertically aligningproperty, the liquid crystal organic semiconductor material can bevertically aligned in the organic semiconductor layer formed on thealignment layer. This matter makes it possible to improve, in theorganic semiconductor layer, the mobility of electric charges in thein-plane direction of the layer. For this reason, the invention makes itpossible to manufacture an organic semiconductor element excellent intransistor properties.

The invention also provides an organic semiconductor element comprising:an alignment layer for aligning a liquid crystal organic semiconductormaterial; a source electrode and a drain electrode formed on thealignment layer; an organic semiconductor layer including the liquidcrystal organic semiconductor material and formed on the alignment layerto cover the source electrode and the drain electrode; and a dielectriclayer formed on the organic semiconductor layer to be positioned atleast on a channel region between the source electrode and the drainelectrode; wherein an aggregate of the liquid crystal organicsemiconductor material is formed on the alignment layer to be positionedin a dielectric-layer-nonformed region where the dielectric layer is notformed.

According to the invention, the aggregate of the liquid crystal organicsemiconductor material is formed on the alignment layer and in thedielectric-layer-nonformed region, so that this region has no organicsemiconductor layer. By contrast, no aggregate of the liquid crystalorganic semiconductor material is formed on the alignment layer and inthe dielectric-layer-formed region thereof, so that this region has theorganic semiconductor layer. Thus, this element can be an organicsemiconductor element in which its organic semiconductor layer issatisfactorily patterned in accordance with whether or not a dielectriclayer is formed on the organic semiconductor layer. Additionally, in theorganic semiconductor layer formed on the alignment layer for aligningthe liquid crystal organic semiconductor material, this liquid crystalsemiconductor material can be aligned so that the organic semiconductorlayer can be improved in mobility. Accordingly, this element can be anorganic semiconductor element excellent in transistor properties.

In the invention, it is allowable that an electrode laminated bodyhaving a substrate, a gate electrode formed on the substrate, and a gateinsulating layer formed on the substrate to cover the gate electrode,wherein the alignment layer is formed on the gate insulating layer ofthe electrode laminated body. When the organic semiconductor element ofthe invention has this structure, the organic semiconductor element canbe rendered an organic semiconductor element of abottom-gate/bottom-contact type.

Advantageous Effects of Invention

The invention produces an advantageous effect capable of yielding anorganic semiconductor element in which an organic semiconductor layer iseasily patterned without being lowered in mobility.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1F are a process chart illustrating an example of theorganic semiconductor element manufacturing method of the invention.

FIGS. 2A to 2G are a process chart illustrating another example of theorganic semiconductor element manufacturing method of the invention.

FIG. 3 is a schematic sectional view illustrating an example of theorganic semiconductor element of the invention.

FIG. 4 is a schematic sectional view illustrating a different example ofthe organic semiconductor element of the invention.

FIG. 5 is a schematic sectional view illustrating a different example ofthe organic semiconductor element of the invention.

FIG. 6 is a schematic sectional view illustrating a different example ofthe organic semiconductor element of the invention.

FIG. 7 is a schematic sectional view illustrating a different example ofthe organic semiconductor element of the invention.

FIG. 8 is a graph showing an observation result of any one out oforganic semiconductor elements manufactured in Example 1.

FIG. 9 is a graph showing evaluation results of transistor properties ofthe organic semiconductor elements manufactured in Example 1.

FIG. 10 is a graph showing evaluation results of transistor propertiesof organic semiconductor elements manufactured in Comparative Example 1.

FIG. 11 is a graph showing evaluation results of transistor propertiesof organic semiconductor elements manufactured in Example 2.

FIG. 12 is a graph showing evaluation results of transistor propertiesof organic semiconductor elements manufactured in Comparative Example 2.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a detailed description will be made about the method of theinvention for manufacturing an organic semiconductor element, and theorganic semiconductor element thereof.

A. Method for Manufacturing an Organic Semiconductor Element

First, the method of the invention for manufacturing an organicsemiconductor element is described. The organic semiconductor elementmanufacturing method of the invention comprises steps of: a sourceelectrode and drain electrode formation step of forming a sourceelectrode and a drain electrode on an alignment layer for aligning aliquid crystal organic semiconductor material; an organic semiconductorlayer formation step of forming an organic semiconductor layer havingthe liquid crystal organic semiconductor material on the alignment layerto cover the source electrode and the drain electrode; a dielectriclayer formation step of forming a dielectric layer on the organicsemiconductor layer to be positioned at least on a channel regionbetween the source electrode and the drain electrode; and an annealingstep of annealing the organic semiconductor layer, on which thedielectric layer is formed, at a liquid crystal phase temperature of theliquid crystal organic semiconductor material.

With reference to some of the drawings, the organic semiconductorelement manufacturing method of the invention is described. FIGS. 1A to1F are a process chart illustrating an example of the organicsemiconductor element manufacturing method of the invention. Asillustrated in FIGS. 1A to 1F, in this organic semiconductor elementmanufacturing method according to the invention, an electrode laminatedbody 14 is used which has a substrate 11, a gate electrode 12 formed onthe substrate 11, and a gate insulating layer 13 formed on the substrate11 to cover the gate electrode 12 (FIG. 1A). This manufacturing methodfurther comprises: an alignment layer formation step (FIG. 1B) offorming an alignment layer 1 for aligning a liquid crystal organicsemiconductor material on the gate insulating layer 13 of the electrodelaminated body 14; a source electrode and drain electrode formation step(FIG. 1C) of forming a source electrode 2 and a drain electrode 3 on thealignment layer 1; an organic semiconductor layer formation step (FIG.1D) of forming, on the alignment layer 1, an organic semiconductor layer4 having the liquid crystal organic semiconductor material to cover thesource electrode 2 and the drain electrode 3; a dielectric layerformation step (FIG. 1E) of forming a dielectric layer 5 on the organicsemiconductor layer 4 to be positioned at least on a channel region Cbetween the source electrode 2 and the drain electrode 3; and anannealing step (not illustrated) of annealing the organic semiconductorlayer 4, on which the dielectric layer 5 is formed, a of liquid crystalphase temperature of the liquid crystal organic semiconductor material.In this way, an organic semiconductor element 10 is manufactured (FIG.1F). Furthermore, as illustrated in FIG. 1F, in the organicsemiconductor element 10 manufactured by the organic semiconductorelement manufacturing method according to the invention, grains of anaggregate 6 of the liquid crystal organic semiconductor material areformed on the alignment layer 1 to be positioned in adielectric-layer-nonformed region X of the alignment layer 1, where thedielectric layer 5 is not formed.

According to the invention, the annealing step is performed, whereby theaggregate of the liquid crystal organic semiconductor material is formedon the alignment layer and in the dielectric-layer-nonformed region, sothat this region has no organic semiconductor layer. By contrast, noaggregate of the liquid crystal organic semiconductor material is formedon the alignment layer and in the dielectric-layer-formed regionthereof, so that this region has the organic semiconductor layer. Thus,the organic semiconductor layer can easily be patterned without beinglowered in mobility. Additionally, the workpiece is annealed at theliquid crystal phase temperature; thus, in the organic semiconductorlayer, the aligning treatment of the liquid crystal organicsemiconductor material can be simultaneously attained.

The organic semiconductor element manufacturing method of the inventioncomprises at least the source electrode and drain electrode formationstep, the organic semiconductor layer formation step, the dielectriclayer formation step, and the annealing step. If necessary, the methodmay comprise one or more optional different steps.

Hereinafter, a description will be made about each of the steps in theorganic semiconductor element manufacturing method of the invention.

1. Source Electrode and Drain Electrode Formation Step

First, a description is made about the source electrode and drainelectrode formation step in the invention. The step is a step of forminga source electrode and a drain electrode on an alignment layer foraligning a liquid crystal organic semiconductor material.

The alignment layer used in the step is a layer having a function foraligning a liquid crystal organic semiconductor material. The alignmentlayer is not particularly limited as far as the layer is a layer makingit possible to align a liquid crystal organic semiconductor materialcontained in an organic semiconductor layer to be formed in the organicsemiconductor layer formation step, which will be detailed later. Inaccordance with the species of the liquid crystal organic semiconductormaterial, the alignment layer is appropriately selected to be usable.Examples of this alignment layer include a parallel alignment membranefor aligning the liquid crystal organic semiconductor material on thealignment layer in parallel to the front surface of the alignment layer,and a vertical alignment membrane for aligning the liquid crystalorganic semiconductor material on the alignment layer vertically to thefront surface of the alignment layer.

The parallel alignment membrane is not particularly limited as far asthe membrane is a membrane making it possible to align the liquidcrystal organic semiconductor material into the predetermined direction.Examples of the parallel alignment membrane include a rubbed membranesubjected to rubbing treatment to succeed in the supply of a function ofaligning the liquid crystal organic semiconductor material into therubbing direction; and a photo alignment membrane which includes aphotoreactive material and is irradiated with polarized light to succeedin the supply of a function of aligning the liquid crystal organicsemiconductor material into a given direction.

Examples of the rubbed membrane include membranes each made ofpolyimide, polyamide, polyvinyl alcohol, polyvinyl phenol, polyester ornylon.

Examples of the photo alignment membrane include membranes each made ofpolyimide, polyamide or polyvinyl cinnamate.

The above-mentioned vertical alignment membrane is not particularlylimited as far as the membrane is a membrane making it possible to alignthe liquid crystal organic semiconductor material in a directionvertical to the front surface of the alignment layer. Examples of thevertical alignment membrane include membranes each made of polyimide,fluoropolymer, a silane coupling agent, or silicone polymer.

As the alignment layer used in the step, either the parallel alignmentmembrane or the vertical alignment membrane is preferably usable. It isparticularly preferred to use, out of the two, the vertical alignmentmembrane. The use of the vertical alignment membrane as the alignmentlayer makes it possible to improve the mobility in the in-planedirection of the organic semiconductor layer formed on the alignmentlayer to improve the transistor performance of the organic semiconductorelement manufactured by the invention.

The thickness of the alignment layer used in the step is notparticularly limited as far as the thickness is within a rangepermitting the layer to gain a desired aligning function in accordancewith the species of the alignment membrane used as the alignment layer,and other factors. Usually, the thickness ranges preferably from 1 nm to1 μm, more preferably from 1 nm to 0.5 μm, and even more preferably from1 nm to 0.1 μm.

The source electrode and the drain electrode used in the step areelectrodes formed on the alignment layer to be usually opposed to eachother at a given interval. The interval set between the source electrodeand the drain electrode creates a channel region. The constituentmaterial of the source electrode and the drain electrode is notparticularly limited as far as the material is a conductive materialhaving a desired conductivity. Examples of the conductive materialinclude inorganic materials such as Ta, Ti, Al, Zr, Cr, Nb, Hf, Mo, Au,Ag, Pt, Cu, Mo—Ta alloy, ITO (indium tin oxide), and IZO (indium zincoxide); and conductive organic materials such as PEDOT/PSS (polyethylenedioxythiophene/polystyrene sulfonic acid). The source electrode and thedrain electrode may be made of a single conductive material or two ormore conductive materials. In the source electrode and the drainelectrode, the same conductive material may be used, or conductivematerials different from each other may be used.

In the step, the method for forming the source electrode and the drainelectrode is not particularly limited as far as the method makes itpossible to form each of the source electrode and the drain electrode tohave a shape decided in advance, using a desired conductive material.Examples of the method include CVD methods such as plasma CVD, thermalCVD and laser CVD, PVD methods such as vacuum deposition, sputtering andion plating, and other dry methods; and electroplating, immersionplating, electroless plating, a sol-gel method, a metal organicdecomposition (MOD) method, spin coating, blade coating, dipping, spraycoating, ink-jetting, flexography, micro-contact printing, screenprinting, offset printing, gravure printing, and other wet methods.

Between the source electrode and the drain electrode formed through thestep, a channel region is formed. Usually, the distance between thesource electrode and the drain electrode ranges preferably from 0.1 μmto 1 mm, more preferably from 0.5 μm to 200 μm, and even more preferablyfrom 1 μm to 100 μm.

The thickness of the source electrode and the drain electrode formedthrough the step is not particularly limited as far as the thickness iswithin a range permitting the electrodes to attain a desired electricresistance in accordance with the species of the used conductivematerial. Usually, the thickness ranges preferably from 1 nm to 1 μm,more preferably from 10 nm to 200 nm, and even more preferably from 20nm to 100 nm.

2. Organic Semiconductor Layer Formation Step

The following describes the organic semiconductor layer formation stepin the invention. The step is a step of forming an organic semiconductorlayer having a liquid crystal organic semiconductor material on thealignment layer to cover the source electrode and the drain electrode.

The organic semiconductor layer formed through the step is a layerhaving a liquid crystal organic semiconductor material. The liquidcrystal organic semiconductor material used in the step is notparticularly limited as far as the material is a material havingsemiconductor properties, and exhibiting a liquid crystal phase at apredetermined temperature. The material is appropriately selected inaccordance with factors such as a use purpose of the organicsemiconductor element manufactured by the invention, so as to be usable.In particular, about the liquid crystal organic semiconductor materialused in the step, liquid crystal phase temperatures thereof, at whichthe material exhibits a liquid crystal phase, are preferably 450° C. andlower, more preferably 300° C. and lower, and even more preferably 200°C. and lower. The liquid crystal phase temperatures are usually 40° C.and higher.

The liquid crystal phase temperatures mean temperatures at which theliquid crystal organic semiconductor material exhibits a liquid crystalphase. The liquid crystal phase temperatures are measurable by, forexample, thermal analysis by differential scanning calorimetry (DSC), ortexture observation through a polarizing microscope.

The liquid crystal organic semiconductor material used in the step canbe classified into a high-molecular-weight liquid crystal organicsemiconductor material and a low-molecular-weight liquid crystal organicsemiconductor material. In the step, either the high-molecular-weightliquid crystal organic semiconductor material or thelow-molecular-weight liquid crystal organic semiconductor material ispreferably usable.

Examples of the high-molecular-weight liquid crystal organicsemiconductor material include polythiophene derivatives, polyphenylenederivatives, polyaniline derivatives, polyphenylene vinylenederivatives, polythienylenevinylene derivatives, polyacetylenederivatives, polydiacetylene derivatives, polytriphenylaminederivatives, copolymer derivatives each made from triphenylamine andphenylenevinylene, copolymer derivatives each made from thiophene andphenylene, copolymer derivatives each made from thiophene andthienothiophene, and copolymer derivatives each made from thiophene andfluorene.

Examples of the low-molecular-weight liquid crystal organicsemiconductor material include oligochalcogenophene derivatives,oligophenylene derivatives, cooligomer derivatives each made fromchalcogenophene and phenylene, condensed cyclic compound derivatives ofchalcogenophene, such as tetrathienoacene, condensed cyclic compoundderivatives each made from chalcogenophene and phenylene, condensedpolycyclic hydrocarbon derivatives such as anthracene, tetracene,pentacene, pyrene, triphenylene and coronene, cooligomer derivativeseach made from chalcogenophene and a condensed polycyclic hydrocarbon,phthalocyanine derivatives, porphyrin derivatives, tetrathiofulvalenederivatives, triphenylamine derivatives, tetracyanoquinodimethanederivatives, benzoquinone derivatives, thiazolothiazole derivatives,anthradithiophene derivatives, benzothienobenzothiophene derivatives,dinaphthothienothiophene derivatives, and fullerene derivatives.

In the invention, the liquid crystal organic semiconductor material usedin the step is in particular preferably the low-molecular-weight liquidcrystal organic semiconductor material.

About the liquid crystal organic semiconductor material, only a singlespecies thereof, or two or more species thereof may be used in the step.

The method for forming the organic semiconductor layer in the step isnot particularly limited as far as the method is a method capable offorming this layer as a desired organic semiconductor layer at least onthe alignment layer on which the source electrode and the drainelectrode are formed to cover the source electrode and the drainelectrode. Examples of this method include spin coating, blade coating,dipping, spray coating, ink-jetting, flexography, micro-contactprinting, screen printing, offset printing and gravure printing in eachof which an organic-semiconductor-layer-forming coating liquid thatcontains a liquid crystal organic semiconductor material is used andthis coating liquid is coated onto the whole of the surface of thealignment layer on which the source electrode and the drain electrodeare formed.

The thickness of the organic semiconductor layer formed through the stepis not particularly limited as far as the thickness is within a rangepermitting the formed organic semiconductor layer to have a desiredsemiconductor property in accordance with the species of the organicsemiconductor material, and other factors. Usually, the thickness rangespreferably from 1 nm to 1000 nm, more preferably from 5 nm to 500 nm,and even more preferably from 10 nm to 300 nm.

3. Dielectric Layer Formation Step

The following describes the dielectric layer formation step in theinvention. The step is a step of forming a dielectric layer on theorganic semiconductor layer to be positioned at least on a channelregion between the source electrode and the drain electrode.

The material of the dielectric layer used in the step is notparticularly limited as far as the material is a material which hasinsulating performance, and does not invade the organic semiconductorlayer. Examples of the material include fluororesins such as PTFE™ andCYTOP™ (manufactured by Asahi Glass Co., Ltd.), acrylic resins, phenolicresins, epoxy resins, cardo resins, vinyl resins, imide resins, andnovolak resins. Among these examples, fluororesins are preferred, whichare soluble in a fluorine-containing solvent that does not produce anyeffect at all onto the organic semiconductor layer. About the materialof the dielectric layer, only a single species thereof, or two or morespecies thereof may be used in the step.

The method for forming the dielectric layer in the step is notparticularly limited as far as the method makes it possible to form thislayer as a desired dielectric layer on the organic semiconductor layerto be positioned at least on the channel region between the sourceelectrode and the drain electrode. Examples of the method include amethod of using a dielectric-layer-forming coating liquid containing amaterial of the dielectric layer, and a solvent which does not produceany effect onto the organic semiconductor layer, such as afluorine-containing solvent, and coating this coating liquid onto theorganic semiconductor layer by a printing method such as screenprinting; and a method of using a target of a material of the dielectriclayer, and depositing the material onto the organic semiconductor layerby a CVD method such as plasma CVD, thermal CVD or laser CVD, or a vapordeposition method such as vacuum deposition, sputtering or ion plating.

The thickness of the dielectric layer formed through the step is notparticularly limited as far as the thickness is within a rangepermitting, in the annealing step, which will be detailed later, theprevention of both the outflow of the organic semiconductor layer andthe formation of an aggregate of the liquid crystal organicsemiconductor material. Usually, the thickness ranges preferably from 10nm to 100 μm, more preferably from 50 nm to 10 μm, and even morepreferably from 100 nm to 1 μm.

4. Annealing Step

The following describes the annealing step. The step is a step ofannealing the organic semiconductor layer on which the dielectric layeris formed at the liquid crystal phase temperature of the liquid crystalorganic semiconductor material. By performing the step, an aggregate ofthe liquid crystal organic semiconductor material is formed on thealignment layer to be positioned in a dielectric-layer-nonformed regionwhere the dielectric layer is not formed. In this way, the organicsemiconductor layer can easily be patterned without being lowered inmobility.

The reason why the organic semiconductor layer can easily be patternedwithout being lowered in mobility through the step would be as follows.About the organic semiconductor layer of the region where the dielectriclayer is formed, the liquid crystal organic semiconductor material isnot caused to flow out by surface tension even when the liquid crystalorganic semiconductor material comes to have fluidity by the annealingat the liquid crystal phase temperature; this is because the organicsemiconductor layer has, on the front surface thereof, the dielectriclayer. Thus, the organic semiconductor layer can keep the thin-film-formthereof. By contrast, about the organic semiconductor layer of theregion where the dielectric layer is not formed, the front surface ofthe organic semiconductor layer is lost when the liquid crystal organicsemiconductor material comes to have fluidity by the annealing at theliquid crystal phase temperature. Thus, the liquid crystal organicsemiconductor material flows out so that the organic semiconductor layercannot keep the thin-film-form thereof. Consequently, an aggregatethereof is formed. As a result, the organic semiconductor layer can beautomatically patterned without being lowered in mobility.

Since the annealing is performed at the liquid crystal phasetemperature, the alignment treatment of the liquid crystal organicsemiconductor material can also be simultaneously made in the organicsemiconductor layer. This matter makes it possible to arrange the liquidcrystal organic semiconductor material regularly in the organicsemiconductor layer to improve the mobility of the organic semiconductorlayer. In the invention, the organic semiconductor layer is formed onthe alignment layer for aligning the liquid crystal organicsemiconductor material; it is therefore possible to stabilize thealignment property of the liquid crystal organic semiconductor materialin the organic semiconductor layer even after the annealing.

The method for the annealing that is used in the step is characterizedby annealing the organic semiconductor layer on which the dielectriclayer is formed at the liquid crystal phase temperature of the liquidcrystal organic semiconductor material. The liquid crystal phasetemperature is the same as described in the subitem “2. Organicsemiconductor layer formation step”; thus, any description thereabout isomitted herein.

The annealing temperature in the step is not particularly limited as faras the temperature is within the liquid crystal phase temperatures.Specifically, the annealing temperature can be appropriately decided inaccordance with the species of the liquid crystal organic semiconductormaterial, and other factors.

The annealing period in the step is not particularly limited as far asthe period makes it possible to form the aggregate of the liquid crystalorganic semiconductor material on the alignment layer to be positionedin the dielectric-layer-nonformed region where the dielectric layer isnot formed. Specifically, the annealing period can be appropriatelydecided in accordance with the species of the liquid crystal organicsemiconductor material, and other factors. Usually, the period rangesfrom 1 second to 24 hours.

The atmosphere for the annealing in the step is, for example, anatmospheric atmosphere, an inert gas atmosphere such as nitrogen gas orargon gas, or a vacuum. Among these atmospheres, atmospheric, and inertgas atmospheres are preferred.

By performing the step in the invention, an aggregate of the liquidcrystal organic semiconductor material are formed on the alignment layerto be usually positioned in the dielectric-layer-nonformed region wherethe dielectric layer is not formed. The form of the aggregate is, forexample, a granular form. When the aggregate is granular, usually, theaverage grain diameter thereof is preferably 1000 μm or less, morepreferably 100 μm or less, even more preferably 10 μm or less althoughthe diameter is not particularly limited. The average particle diameteris measurable by, for example, observation through a polarizingmicroscope.

5. Different Step(s)

The organic semiconductor element manufacturing method of the inventioncomprises at least the source electrode and drain electrode formationstep, the organic semiconductor layer formation step, the dielectriclayer formation step, and the annealing step. If necessary, the methodmay comprise one or more different steps. The different step(s) used inthe invention is/are not particularly limited, and may be (each) anystep in accordance with a use purpose of the organic semiconductorelement manufactured in the invention, and other factors. As thedifferent step, the invention may have, before the source electrode anddrain electrode formation step, the alignment layer formation step,which is a step of using an electrode laminated body having a substrate,a gate electrode formed on the substrate and a gate insulating layerformed on the substrate to cover the gate electrode, and forming theabove-mentioned alignment layer onto the gate insulating layer of theelectrode laminated body. When the invention has the alignment layerformation step, an organic semiconductor element of abottom-gate/bottom-contact type can be formed.

When the organic semiconductor element manufacturing method of theinvention comprises the alignment layer formation step, for example, thefollowing are performed as has been illustrated in FIGS. 1A to 1F. Theelectrode laminated body 14 is used, which has the substrate 11, thegate electrode 12 formed on the substrate 11, and the gate insulatinglayer 13 formed on the substrate 11 to cover the gate electrode 12 (FIG.1A). The alignment layer 1 for aligning a liquid crystal organicsemiconductor material is formed on the gate insulating layer 13 of theelectrode laminated body 14 (FIG. 1B, alignment layer formation step).The source electrode 2 and the drain electrode 3 are formed on thealignment layer 1 (FIG. 1C, source electrode and drain electrodeformation step). The organic semiconductor layer 4 is formed to coverthe source electrode 2 and the drain electrode 3 (FIG. 1D, organicsemiconductor layer formation step). The dielectric layer 5 is formed onthe organic semiconductor layer 4 to be positioned at least on thechannel region C between the source electrode 2 and the drain electrode3 (FIG. 1E, dielectric layer formation step). The organic semiconductorlayer 4, on which the dielectric layer 5 is formed, is annealed at theliquid crystal phase temperature of the liquid crystal organicsemiconductor material (not illustrated, annealing step). In this way,the organic semiconductor element 10 is manufactured (FIG. 1F). At thistime, in the organic semiconductor element 10 illustrated in FIG. 1F,the grains of the aggregate 6 of the liquid crystal organicsemiconductor material are formed on the alignment layer 1 to bepositioned in the dielectric-layer-nonformed region X of the alignmentlayer 1, where the dielectric layer 5 is not formed.

The substrate used in the electrode laminated body is not particularlylimited, and may be appropriately decided in accordance with a usepurpose of the organic semiconductor element manufactured according tothe invention, and other factors. Accordingly, the substrate may be aflexible substrate, which has flexibility, or may be a rigid substrate,which has no flexibility. Specific examples of the substrate includesubstrates each made of polyimide, polyethylene naphthalate,polyethylene terephthalate, polyethersulfone, polycarbonate,polyetherimide, polyetheretherketone, polyetherketone, polyphenylenesulfide, liquid crystal polymer, epoxy resin, silicone resin, orphenolic resin; a glass substrate; and a SUS substrate.

The thickness of the substrate is appropriately decided in accordancewith the species of the substrate, and other factors. Usually, thethickness is preferably 1 mm or less, and ranges in particularpreferably from 1 μm to 70 μm.

The gate electrode used in the electrode laminated body is an electrodeformed on the substrate. The gate electrode is usually formed into apredetermined pattern on the substrate. The gate electrode is notparticularly limited as far as the electrode is made of a conductivematerial having a desired conductivity. The material may be a conductivematerial that is generally used for a gate electrode of an organictransistor. Examples of the conductive material include inorganicmaterials such as Ta, Ti, Al, Zr, Cr, Nb, Hf, Mo, Au, Ag, Pt, Mo—Taalloy, ITO, and IZO; and conductive organic materials such as PEDOT/PSS.

The thickness of the gate electrode is appropriately decided within arange permitting the electrode to attain a desired conductivity inaccordance with the species of the conductive material used to form thegate electrode, and other factors. Usually, the thickness rangespreferably from 10 nm to 1 μm.

The gate insulating layer used in the electrode laminated body is alayer formed on the substrate to cover the gate electrode. This layer isalso a layer having a function of insulating the source electrode andthe drain electrode electrically from the gate electrode in the organicsemiconductor element manufactured according to the invention. Thematerial constituting the gate insulating layer is not particularlylimited as far as the material is an insulating material having adesired insulating performance. Examples of the insulating materialinclude organic materials such as acrylic resins, phenolic resins,fluororesins, epoxy resins, cardo resins, vinyl resins, imide resins,novolak resins, and polyparaxylene; and inorganic materials such as SiO₂(silicon dioxide), SiN_(x) (silicon nitride), and Al₂O₃ (aluminumoxide). About the insulating material, only a single species thereof, ortwo or more species thereof may be used in the gate insulating layer.

The thickness of the gate insulating layer is appropriately decidedwithin a range permitting the layer to attain a desired insulatingperformance in accordance with the species of the insulating materialused to form the gate insulating layer, and other factors. Usually, thethickness ranges preferably from 10 nm to 5 μm.

The method for forming the alignment layer in the alignment layerformation step is not particularly limited as far as the method is amethod making it possible to form the layer as a layer for aligning theliquid crystal organic semiconductor material into a desired direction.Examples of the method include spin coating, blade coating, dipping,immersing, spray coating, ink-jetting, flexographic, micro-contactprinting, screen printing, offset printing and gravure printing methods.

In the alignment layer formation step, the constituent material used toform the alignment layer, and the thickness of the formed alignmentlayer are the same as described in the item “A. Method for manufacturingan organic semiconductor element”; thus, any description thereabout isomitted herein.

As the above-mentioned different steps, the invention may comprise thefollowing steps: the alignment layer formation step, which is a step ofusing a substrate and forming the above-mentioned alignment layer ontothe substrate, before the organic semiconductor layer formation step;and a gate electrode formation step of forming a gate electrode on theabove-mentioned dielectric layer between the dielectric layer formationstep and the annealing step. When the invention has the alignment layerformation step and the gate electrode formation step, an organicsemiconductor element of a top-gate/bottom-contact type can be formed.

When the organic semiconductor element manufacturing method of theinvention comprises the alignment layer formation step and the gateelectrode formation step, for example, the following are performed asillustrated in FIGS. 2A to 2G. A substrate 11 is used (FIG. 2A), and analignment layer 1 for aligning a liquid crystal organic semiconductormaterial is formed on the substrate 11 (FIG. 2B, alignment layerformation step). A source electrode 2 and a drain electrode 3 are formedon the alignment layer 1 (FIG. 2C, source electrode and drain electrodeformation step), and then an organic semiconductor layer 4 is formed tocover the source electrode 2 and the drain electrode 3 (FIG. 2D, organicsemiconductor layer formation step). A dielectric layer 5 is formed onthe organic semiconductor layer 4 to be positioned at least on a channelregion C between the source electrode 2 and the drain electrode 3 (FIG.2E, dielectric layer formation step), and then a gate electrode 12 isformed on the dielectric layer 5 (FIG. 2F, gate electrode formationstep). The organic semiconductor layer 4, on which the dielectric layer5 and the gate electrode 12 are formed, is annealed at the liquidcrystal phase temperature of the liquid crystal organic semiconductormaterial (not illustrated, annealing step). In this way, an organicsemiconductor element 10 is manufactured (FIG. 2G). At this time, in theorganic semiconductor element 10 illustrated in FIG. 2G, grains of anaggregate 6 of the liquid crystal organic semiconductor material areformed on the alignment layer 1 to be positioned in adielectric-layer-nonformed-region X of the alignment layer 1, where thedielectric layer 5 is not formed. FIGS. 2A to 2G are a process chartillustrating this example, which is a different example of the organicsemiconductor element manufacturing method of the invention.

In the alignment layer formation step, the respective materials of theused substrate and alignment layer, the method for forming the alignmentlayer, and thickness of the formed alignment layer are the same asdescribed above.

The method for forming the gate electrode in the gate formation step isnot particularly limited as far as the method is a method making itpossible to form the gate electrode to have a shape decided in advance,using a desired conductive material. Examples of the method include CVDmethods such as plasma CVD, thermal CVD and laser CVD, PVD methods suchas vacuum deposition, sputtering and ion plating, and other dry methods;and electroplating, immersion plating, electroless plating, a sol-gelmethod, a metal organic decomposition (MOD) method, spin coating, bladecoating, dipping, spray coating, ink-jetting, flexography, micro-contactprinting, screen printing, offset printing, gravure printing, and otherwet methods.

In the gate electrode formation step, the constituent material used toform the gate electrode, and the thickness of the formed gate electrodeare the same as described above. In the invention, the manufacturingmethod may comprise the gate electrode formation step after theannealing step.

Furthermore, the invention may comprise, as the above-mentioneddifferent step, a passivation layer formation step of forming apassivation layer on the organic semiconductor layer to cover thedielectric layer between the dielectric layer formation step and theannealing step, or after the annealing step. By the formation of thepassivation layer, which has a function of preventing a deterioration ofthe organic semiconductor element with time, the organic semiconductorelement manufactured by the invention can be rendered an elementexcellent in durability.

The constituent material of the passivation layer used in thepassivation layer formation step is not particularly limited as far asthe material is a material making it possible to prevent, into a desireddegree, the exposure of the organic semiconductor layer to water andothers contained in the air in the organic semiconductor elementmanufactured by the invention. Examples of the material include acrylicresins, phenolic resins, fluororesins, epoxy resins, cardo resins, vinylresins, vinyl acetate resins, imide resins, and novolak resins.

The method for forming the passivation layer in the passivation layerformation step is not particularly limited as far as the method is amethod making it possible to form the layer as a desired passivationlayer on the organic semiconductor layer to cover the dielectric layer.Examples of the method include a wet method of using apassivation-layer-forming coating liquid which contains a constituentmaterial of the passivation layer and a solvent which does not invadethe material of the dielectric layer, and coating this coating liquidonto the organic semiconductor layer by a printing method, such asscreen printing, to cover the dielectric layer; and a dry method ofpressing and bonding the passivation layer thermally onto the organicsemiconductor layer at a temperature and a pressure that do not permitthe passivation layer to invade the respective materials of the organicsemiconductor layer and the dielectric layer, so as to cover thedielectric layer.

The thickness of the passivation layer formed through the passivationlayer formation step is not particularly limited, and is appropriatelydecided within a range permitting the layer to realize a desireddurability in accordance with the species of the constituent materialthereof, and other factors. Usually, the thickness ranges preferablyfrom 1 μm to 50 μm.

B. Organic Semiconductor Element

The following describes the organic semiconductor element of theinvention. The organic semiconductor element of the invention is anelement comprising: an alignment layer for aligning a liquid crystalorganic semiconductor material; a source electrode and a drain electrodeformed on the alignment layer; an organic semiconductor layer having theliquid crystal organic semiconductor material and formed on thealignment layer to cover the source electrode and the drain electrode;and a dielectric layer formed on the organic semiconductor layer to bepositioned at least on a channel region between the source electrode andthe drain electrode; wherein an aggregate of the liquid crystal organicsemiconductor material is formed on the alignment layer to be positionedin a dielectric-layer-nonformed region where the dielectric layer is notformed.

With reference to some of the drawings, the organic semiconductorelement of the invention is described. FIG. 3 is a schematic sectionalview illustrating an example of the organic semiconductor element of theinvention. As illustrated in FIG. 3, an organic semiconductor element 10of the invention comprises an electrode laminated body 14 having asubstrate 11, a gate electrode 12 formed on the substrate 11 and a gateinsulating layer 13 formed on the substrate 11 to cover the gateelectrode 12; an alignment layer 1 formed on the gate insulating layer13 of the electrode laminated body 14 to align a liquid crystal organicsemiconductor material; a source electrode 2 and a drain electrode 3formed on the alignment layer 1; an organic semiconductor layer 4 havingthe liquid crystal organic semiconductor material and formed on thealignment layer 1 to cover the source electrode 2 and the drainelectrode 3; and a dielectric layer 5 formed on the organicsemiconductor layer 4 to be positioned at least on a channel region Cbetween the source electrode 2 and the drain electrode 3. In the organicsemiconductor element 10 illustrated in FIG. 3, gains of an aggregate 6of the liquid crystal organic semiconductor material are formed on thealignment layer 1 to be positioned in a dielectric-layer-nonformedregion X of the alignment layer 1, where the dielectric layer 5 is notformed.

According to the invention, the aggregate of the liquid crystal organicsemiconductor material is formed on the alignment layer and in thedielectric-layer-nonformed region, so that this region has no organicsemiconductor layer. By contrast, no aggregate of the liquid crystalorganic semiconductor material is formed on the alignment layer and inthe dielectric-layer-formed region thereof, so that this region has theorganic semiconductor layer. Thus, this element can be an organicsemiconductor element in which its organic semiconductor layer issatisfactorily patterned in accordance with whether or not a dielectriclayer is formed on the organic semiconductor layer. Additionally, in theorganic semiconductor layer formed on the alignment layer for aligningthe liquid crystal organic semiconductor material, this material can bealigned so that the organic semiconductor layer can be improved inmobility. Accordingly, this element can be an organic semiconductorelement excellent in transistor properties.

The organic semiconductor element of the invention comprises at leastthe alignment layer, the source electrode and the drain electrode, theorganic semiconductor layer, the dielectric layer, and the aggregate. Ifnecessary, the element may comprise one or more different constituents.

Hereinafter, a description will be made about each of the constituentsof the organic semiconductor element of the invention.

1. Organic Semiconductor Layer

First, the organic semiconductor layer in the invention is described.The organic semiconductor layer in the invention is a layer formed on analignment layer to cover a source electrode and a drain electrode, andhaving a liquid crystal organic semiconductor material. The liquidcrystal organic semiconductor material used in the invention is the sameas described in the item “A. Method for manufacturing an organicsemiconductor element”; thus, any description thereabout is omittedherein. The thickness and others of the organic semiconductor layer usedin the invention are also the same as described in the item “A. Methodfor manufacturing an organic semiconductor element”.

2. Dielectric Layer

The following describes the dielectric layer in the invention. Thedielectric layer in the invention is a layer formed on the organicsemiconductor layer to be positioned at least on a channel regionbetween the source electrode and the drain electrode. The material, thethickness, and others of the dielectric layer used in the invention arethe same as described in the item “A. Method for manufacturing anorganic semiconductor element”; thus, any description thereabout isomitted herein.

3. Aggregate

The following describes the aggregate in the invention. The aggregate inthe invention is a material formed on the alignment layer to bepositioned in the dielectric-layer-nonformed region thereof, where nodielectric layer is formed, and is a material about which the liquidcrystal organic semiconductor material aggregates. Details of theaggregate in the invention are the same as described in the item “A.Method for manufacturing an organic semiconductor element”; thus, anydescription thereabout is omitted herein.

4. Alignment Layer

The following describes the alignment layer in the invention. Thealignment layer in the invention is a layer for aligning a liquidcrystal organic semiconductor material. The material, the thickness andothers of the alignment layer used in the invention are the same asdescribed in the item “A. Method for manufacturing an organicsemiconductor element”; thus, any description thereabout is omittedherein.

5. Source Electrode and Drain Electrode

The following describes the source electrode and the drain electrode inthe invention. The source electrode and the drain electrode in theinvention are electrodes formed on the alignment layer to be usuallyopposed to each other at a given interval therebetween. The interval setbetween the source electrode and the drain electrode creates a channelregion. The material, the thickness and others of the source electrodeand the drain electrode used in the invention, and the distance betweenthe source electrode and the drain electrode are the same as describedin the item “A. Method for manufacturing an organic semiconductorelement”; thus, any description thereabout is omitted herein.

6. Organic Semiconductor Element

The organic semiconductor element of the invention comprises at leastthe alignment layer, the source electrode and the drain electrode, theorganic semiconductor layer, the dielectric layer, and the aggregate. Ifnecessary, the element may comprise one or more different constituents.The different constituent(s) used in the invention is/are notparticularly limited. In accordance with a use purpose of the organicsemiconductor element of the invention, the organic semiconductorelement manufacturing method of the invention, and other factors, one ormore constituents having a desired function are appropriately selectedto be usable. In the invention, the different constituents are usually asubstrate, a gate electrode, and a gate insulating layer. The substrate,the gate electrode, and the gate insulating layer are the same asdescribed in the item “A. Method for manufacturing an organicsemiconductor element”; thus, any description thereabout is omittedherein.

In the invention, an electrode laminated body having a substrate, a gateelectrode formed on the substrate, and a gate insulating layer formed onthe substrate to cover the gate electrode may be used, and the alignmentlayer may be formed on the gate insulating layer of this electrodelaminated body. When the organic semiconductor element of the inventionhas this structure, this element can be rendered an organicsemiconductor element of a bottom-gate/bottom-contact type. As has beenillustrated in FIG. 3, in the organic semiconductor element 10 of theinvention, the alignment layer 1 may be formed on the gate insulatinglayer 13 of the electrode laminated body 14, which has the substrate 11,the gate electrode 12 formed on the substrate, and the gate insulatinglayer 13, which is formed on the substrate 11 to cover the gateelectrode 12.

Meantime, it is allowable in the invention to form the above-mentionedalignment layer on a substrate, and form a gate electrode on adielectric layer. When the organic semiconductor element of theinvention has this structure, this element can be rendered an organicsemiconductor element of a top-gate/bottom-contact type. As illustratedin FIG. 4, in an organic semiconductor element 10 of the invention, itis allowable to form an alignment layer 1 on a substrate 11 and form agate electrode 12 on a dielectric layer 5. FIG. 4 is a schematicsectional view illustrating this example, which is a different exampleof the organic semiconductor element of the invention. Reference signsnot referred to herein represent the same members as in FIG. 3,respectively; thus, any description thereabout is omitted herein.

In the invention, the organic semiconductor element may have, as thedifferent constituent, a passivation layer having a function ofpreventing a deterioration of this element with time. The use of thepassivation layer makes it possible to render the organic semiconductorelement of the invention an element excellent in durability. Theconstituent material, the thickness and others of the passivation layerare the same as described in the item “A. Method for manufacturing anorganic semiconductor element”; thus, any description thereabout isomitted herein.

When the organic semiconductor element of the invention is an elementthat is of a bottom-gate/bottom-contact type and has a passivationlayer, it is allowable that as illustrated in FIG. 5, in an organicsemiconductor element 10 of the invention, a passivation layer 15 isformed on an alignment layer 1 to cover a dielectric layer 5 and grainsof an aggregate 6. Meantime, when the organic semiconductor element ofthe invention is an element that is of a top-gate/bottom-contact typeand has a passivation layer, it is allowable that as illustrated in FIG.6, in an organic semiconductor element 10 of the invention, apassivation layer 15 is formed on an alignment layer 1 to cover a gateelectrode 12 and grains of an aggregate 6. It is allowable that asillustrated in FIG. 7, in an organic semiconductor element 10 of theinvention, a passivation layer 15 is formed on an alignment layer 1 tocover a dielectric layer 5 and grains of an aggregate 6 and furtheragate electrode 12 is formed on the passivation layer 15. FIGS. 5 to 7are each a schematic sectional view of one of the examples referred toherein, which is a different example of the organic semiconductorelement of the invention. Reference signs not referred to hereinrepresent the same members as in FIG. 3, respectively; thus, anydescription thereabout is omitted herein.

The organic semiconductor element of the invention may be manufacturedby, for example, the method described in the item “A. Method formanufacturing an organic semiconductor element”.

The invention is not limited to the above-mentioned embodiments. Theembodiments are illustrative examples. Any embodiment that hassubstantially the same structure and produces the same effects andadvantages as any embodiment having the technical conception recited inthe claims of the invention is included in the technical scope of theinvention.

EXAMPLES

Hereinafter, the invention will be specifically described by way ofworking examples.

Example 1 Liquid Crystal Phase Identifying, and Phase TransitionTemperature Checking Experiments

In order to identify/check a liquid crystal phase of5,5″-dioctyl-2,2′:5′,2″-terthiophene (hereinafter referred to as“8-TTP-8”), which is a liquid crystal organic semiconductor material,and the phase transition temperature of this compound, the texturethereof was observed through a polarizing microscope (BH2-UMA™,manufactured by Olympus Corp.) using a heating stage (FP82HT™, FP80HT™,manufactured by Mettler-Toledo International Inc.), and further thiscompound was measured with a DSC (differential scanning calorimeter,DSC204 μ-Sensor™, manufactured by Netzsch Co.). The following resultswere then obtained: Iso: 92.0; SmC: 88.1; SmF: 73.6; SmG: 65.3 cryst. (°C.).

(Formation of an Electrode Laminated Body)

<Substrate, Gate Electrode and Gate Insulating Layer>

A used substrate was an n-heavily-doped silicon wafer, 0.6 mm inthickness, on which a silicon oxide layer of about 3000 angstroms (300nm) thickness was deposited. This was a wafer in which itsn-heavily-doped silicon region functioned as a gate electrode while thesilicon oxide layer functioned as a gate insulating layer. Theelectrostatic capacity thereof was about 11 nF/cm² (nanofarads/squarecentimeter).

(Alignment Layer Formation Step)

The electrode laminated body was immersed in a 0.1-M solution ofn-octyltrichlorosilane (OTS) in dehydrated toluene at 60° C. for 20minutes. Next, this wafer was washed with toluene, acetone, andisopropyl alcohol. A nitrogen gun was used to remove the remainingliquid, and then the resultant was dried at 100° C. for 1 hour to forman alignment layer (thickness: 1 to 2 nm) for aligning a liquid crystalorganic semiconductor material vertically to the front surface thereof.

(Source Electrode and Drain Electrode Formation Step)

By vacuum deposition, Cr was deposited into a thickness of 3 nm and Auwas deposited into a thickness of 27 nm through a shadow mask onto thealignment layer to have a width (W) of 1000 μm and a length (L) of 50nm. In this way, a source electrode and a drain electrode were formed.

(Organic Semiconductor Layer Formation Step)

A chloroform solution containing 4% by weight of the 8-TTP-8, which is aliquid crystal organic semiconductor material, was coated onto thealignment layer by spin coating (at 2000 rpm for 10 seconds) to coverthe source electrode and the drain electrode. In this way, an organicsemiconductor layer of about 100 nm thickness was formed.

(Dielectric Layer Formation Step)

A dielectric-layer-forming coating liquid was prepared in which TeflonAF™ (manufactured by Du Pont-Mitsui Fluorochemicals Co., Ltd.) wasdissolved in FC40™ (manufactured by Sumitomo 3M Ltd.) into aconcentration of 6% by weight. The coating liquid was coated onto theorganic semiconductor element by screen printing to be positioned atleast on a channel region between the source electrode and the drainelectrode. The resultant workpiece was dried at 60° C. for 30 minutes toform a dielectric layer of 550 nm thickness.

(Annealing Step)

In the atmosphere, at 90° C. for 1 minute, the laminated body wasannealed, which was composed of the electrode laminated body, thealignment layer, the source electrode and the drain electrode, theorganic semiconductor layer and the dielectric layer. In this way,organic semiconductor elements were each manufactured.

Comparative Example 1

Organic semiconductor elements were each manufactured in the same way asin Example 1 except that the above-mentioned annealing was notconducted.

Example 2

Organic semiconductor elements were each manufactured in the same way asin Example 1 except that a passivation layer formation step describedbelow was performed between the dielectric layer formation step and theannealing step.

(Passivation Layer Formation Step)

A laminate film (manufactured by Meikoshokai Co., Ltd.) of 100 μmthickness was thermally pressed and bonded onto the organicsemiconductor layer at 90° C. to cover the dielectric layer. In thisway, a passivation layer was formed.

Comparative Example 2

Organic semiconductor elements were each manufactured in the same way asin Example 2 except that the annealing step was not conducted.

[Evaluation]

(Observation of the Organic Semiconductor Elements)

A polarizing microscope was used to observe the organic semiconductorelements manufactured in the above-mentioned working examples andcomparative examples from above these elements (from the dielectriclayer side thereof). In FIG. 8 is shown a result of the observation ofany one of the organic semiconductor elements yielded in Example 1. Asshown in FIG. 8, it was verified that in Example 1, an aggregate of theliquid crystal organic semiconductor material was formed in thedielectric-layer-nonformed region. In Example 2 also, it was verified inthe same way that an aggregate of the liquid crystal organicsemiconductor material was formed in the dielectric-layer-nonformedregion, this situation being not illustrated. By contrast, inComparative Examples 1 and 2, no aggregate of the liquid crystal organicsemiconductor material was verified.

(Transistor Property Evaluation)

About the organic semiconductor elements manufactured in the workingexamples and the comparative examples, transistor properties thereofwere evaluated. The evaluation of the transistor properties was made,using a device, 237 HIGH VOLTAGE SOURCE MEASUREMENT UNIT™, manufacturedby Keithley Instruments Inc. The carrier mobility (μ) (of each of theelements) was calculated in accordance with an equation described below,using data in their saturated region (gate voltage V_(g)<source/drainvoltage V_(sd)). In the equation, I_(d) represents the drain current inthe saturated region; W and L, the width and the length of thesemiconductor channel, respectively; Ci, the electrostatic capacity perunit area of the gate electrode; and V_(g) and V_(th), the gate voltageand the threshold voltage, respectively. The V_(th) of this device wascalculated from a relationship between the square root of the I_(d) inthe saturated region and the V_(g) of the device that was gained byextrapolating I_(d)=0 from measured data.I _(d) =Ciμ(W/2L)(V _(g) −V _(th))²

Results of the evaluation are shown in Table 1 described below. Resultsof the transistor property evaluation of the organic semiconductorelements manufactured in Example 1, Comparative Example 1, Example 2 andComparative Example 2 are shown in FIGS. 9 to 12, respectively. Each ofthe mobilities shown in Table 1 described below is the average value ofthe mobilities of the respective organic semiconductor layers that wereobtained from 5 or more of the transistors (of each of these examples).About conditions for the measurement, the gate voltage V_(g) was appliedin the range of +20 to −40 V and the source/drain voltage V_(sd) wasapplied to give −40 V in the atmosphere. In each of FIGS. 9 to 12, FEMrepresents the (average) mobility of the organic semiconductor layers.

TABLE 1 ON OFF V_(sd) V_(th) MOBILITY CURRENT CURRENT (V) (V) (cm²/Vs)(A) (A) EXAMPLE 1 −40 −4.10 0.0146 1.6 × 10⁻⁶ 2.5 × 10⁻¹² COM- −40 −1.710.0106 1.5 × 10⁻⁶ 1.0 × 10⁻⁹  PARATIVE EXAMPLE 1 EXAMPLE 2 −40 −3.660.0174 2.4 × 10⁻⁶ 3.0 × 10⁻¹² COM- −40 −5.80 0.0178 2.1 × 10⁻⁶ 1.5 ×10⁻⁹  PARATIVE EXAMPLE 2

When FIGS. 9 and 10 are compared with each other, it is verified that inExample 1, the OFF current value thereof was made lower than inComparative Example 1. As shown in Table 1, it is verified that inExample 1, the mobility of the organic semiconductor layers was madebetter than that in Comparative Example 1.

When FIGS. 11 and 12 are compared with each other, similarly, it isverified that in Example 2, the OFF current value thereof was made lowerthan in Comparative Example 2. As shown in Table 1, it is verified thatin Example 2, the mobility of the organic semiconductor layers wassubstantially equivalent to that in Comparative Example 2.

From the above-mentioned results, it can be considered that in themethod of the invention for manufacturing an organic semiconductorelement, its organic semiconductor layer can easily be patterned withoutbeing lowered in mobility through the annealing step.

REFERENCE SIGNS LIST

-   -   1 . . . alignment layer    -   2 . . . source electrode    -   3 . . . drain electrode    -   4 . . . organic semiconductor layer    -   5 . . . dielectric layer    -   6 . . . aggregate    -   10 . . . organic semiconductor element    -   11 . . . substrate    -   12 . . . gate electrode    -   13 . . . gate insulating layer    -   14 . . . electrode laminated body    -   15 . . . passivation layer    -   C . . . channel region    -   X . . . dielectric-layer-nonformed region

The invention claimed is:
 1. A method for manufacturing an organicsemiconductor element, comprising steps of: forming a source electrodeand a drain electrode on an alignment layer for aligning a liquidcrystal organic semiconductor material; forming an organic semiconductorlayer comprising the liquid crystal organic semiconductor material tocover the source electrode and the drain electrode; forming a dielectriclayer on the organic semiconductor layer to be positioned at least on achannel region between the source electrode and the drain electrode; andannealing the organic semiconductor layer at a liquid crystal phasetemperature of the liquid crystal organic semiconductor material to forman aggregate of the liquid crystal organic semiconductor material on thealignment layer in a region where the dielectric layer is not located.2. The method for manufacturing an organic semiconductor elementaccording to claim 1, comprising, before the source electrode and drainelectrode formation step, an alignment layer formation step of using anelectrode laminated body having a substrate, a gate electrode formed onthe substrate and a gate insulating layer on the substrate to cover thegate electrode, and forming the alignment layer on the gate insulatinglayer of the electrode laminated body.
 3. The method for manufacturingan organic semiconductor element according to claim 1, wherein thealignment layer is a layer capable of aligning the liquid crystalorganic semiconductor material vertically.
 4. An organic semiconductorelement, comprising: an alignment layer for aligning a liquid crystalorganic semiconductor material; a source electrode and a drain electrodeformed on the alignment layer; an organic semiconductor layer comprisingthe liquid crystal organic semiconductor material and formed on thealignment layer to cover the source electrode and the drain electrode;and a dielectric layer formed on the organic semiconductor layer atleast on a channel region between the source electrode and the drainelectrode; wherein an aggregate of the liquid crystal organicsemiconductor material is formed on the alignment layer in a regionwhere the dielectric layer is not located.
 5. The organic semiconductorelement according to claim 4, comprising an electrode laminated bodyhaving a substrate, a gate electrode formed on the substrate, and a gateinsulating layer formed on the substrate to cover the gate electrode,wherein the alignment layer is formed on the gate insulating layer ofthe electrode laminated body.